Blast furnace operation



March 13, 1951 LEMS 2,544,697

BLAST FURNACE OPERATION Filed Dec. 31, 1946 INVENTOR WARRENK LEW/5ATTORNEY Patented Mar. 13, 1951 UNITED STATES PATENT A OFFICE BLASTFURNACE OPERATION Warren K. Lewis, Newton, .Mass assignor to StandardOil Development Company, a "corporation of Delaware Application December31, 1946, Serial No. 719,543

to the extent that any change in one which would render the operationmore efficient has the effect of requiring an adjustment of one or moreothers for smooth operation and such adjustment may be in some casesimpossible. In other words, blast furnace operation represents, ofnecessity, a compromise between a plurality of operating factors.

It is generally agreed that the capacity of a blast furnace is limitedabsolutely by'the allowable gas velocity up through the bed withoutblowing out the charge. Capacities have been increased greatly in recentyears by various devices; for example, by sintering to eliminate dustand by using excess pressure at the top of the furnace and by increasingthe content of oxygen in the blast and by combinations of two or more ofthese expedients. It remains true, however, that the capacity limit isset by the velocity that will blow out the charge, the only improvementbeing that these expedients either furnish a charge harder to blow outor reduce the velocity the gas for a given amount of combustion.Thepurpose of the present invention is still further to increase thecapacity of a blast furnace even though it may be using one or all ofthe aforesaid expedients without diminishing in any way the advantagesaccruing from such expedients..

Briefly, the present invention resides in improving the operationof ablast furnace by taking advantage of the excess heat available at thetuyerev level without adversely affecting the temperature at this leveland at the same time increasing the output of pig iron by the furnace.

This is done according to the present invention by separately reducingiron ore and charging it to the blast furnace at the tuyere level.

In order fully to appreciate the advantages of the present invention onemust keep in mind the fact that the blast furnace has a two-foldfunction. It serves to reduce the ore to metal and also serves to meltthe metal produced and separate the molten metal from impurities. Thefirst function is performed fairly easilybut the performance of thesecond function leads to difficulty. The performance of this secondfunction requires high temperature'up to l500' C., and consumes a lot ofheat. In securing this high temperature heat carbon is burned but thenature of the operation is such that the carbon 2 burned can net onlycarbon monoxide, liberating less than one-third of the heat that wouldbe available if one could burn the carbon to carbon dioxide in the usualway. Hence, the carbon is used very inefficiently as a fuel. In fact, asa result of this partial combustion, the large amount of carbon monoxideresulting from the melting (tuyre) zone has a reducing capacity for orefar in excess of the amount of ore coming down the shaft with the coke.Furthermore, because of this low efiiciency of combustion,the heatsupply to the melting zone must be and is enhanced'by preheating the airsupplied as blast.

The quantity of air which may be passed through the pharge is fixed bythe cross-sectional area-of the furnace at a value such that it wontblow out the charge. The quantity of-coke is fixed by this quantity ofair since in the-main this cokemust be burned out at the bottom withair. This coke and this maximum permissible quantity of air preheated tothe maximum temperature attainable from the combustionof the offgasesfrom the blast furnace could reduce a certain quantity of ore. Actually,the amount of ore which can be handled is considerably less, dictated bythe tendency of the furnace to plug when the ratio of ore to cokeexceeds a fairly critical ratio determined by the nature of the ore.

Since the coke is necessary to keep the charge open but only arestricted quantity of ore can be used, and since the temperature attuyere level must not be allowed to rise above a fixed value determinedby the qualities desired in the pig iron, the heat supply at the tuyeresmust be limited by limiting the preheat of the air. In the ordinarycase, this preheat is considerably less than is available from theoff-gases of the furnace by a factor of /2 to A As a result, in thenormal operation of a blast furnace large amounts of potential availablehigh temperature heat are not utilized and the furnace is not used toits potential capacity. This inefficiency is all the more costly becausethe preheat which is wasted in presently used equipment is that whichmay be obtained by complete combustion of the off-gas from the furnaceand by efficient heat exchange which wouldleave the stack gases cool. Asthe operation is presently conducted, much of this cheap heat is lost.Thus the entire operation suffers from the limitations heretoforepointed out.

The present invention minimizes the aforesaid difficulties by imposingan additional heat load on the blast furnace at the tuyere level. Thisheat load is in the form of freshly reduced ore which must be purifiedin any event. By introducing this reduced ore into the blast furnaceadvantage is taken of the surplus heat there available to purify thisore and thereby increase the output of the blast furnace in pig iron. Atthe same time the full heat available as heat of combustion of theoff-gas from the furnace may be utilized more effectively.

The reduced iron ore which is fed to the blast furnace in the region ofthe tuyere level but above the air blast, may be produced by anysuitable method which does not suffer from the aforesaid limitations onthe blast furnace method. In the preferred embodiment of the presentinvention, however, this reduced iron ore is produced by subjectingfinely divided iron ore in a fluidized condition to the action of areducing gas at a suitable temperature. In practicing this type ofreduction the iron ore is ground to a powder, the bulk of which issmaller than 100 mesh and which cont ins particles of various sizesranging upwardly from about 20 microns. This powder is maintained influidized condition in an enlarged reducing zone by passing reducing gasupwardly through it at a velocity between about .5 and 5 ft./second.This operation may be conducted on the .upfiow principle as described inmy Patent No. 2,343,780 issued March '7, 1944, or on the downfiowprinciple as hereinafter described.

Th nature and objects of the present invention will be more fullyunderstood from the following detailed description of the accompanyingdrawing in which the single figure is a front elevation in diagrammaticform of one type of apparatus suitable for the practice of the presentinvention.

Referring to the drawing in detail, numeral I designates a conventionalblast furnace having at its upper end a feed hopper 2 and at its lowerend a crucible portion 3. Just above the crucible portion there areprovided tuyres 4 for the introduction of blast gas into the furnace.The crucible portion is provided with a conventional drawofi 5 formolten pig iron and a drawoff 6 for slag. At the upper end of thefurnace there is an outlet line 1 for gas. This line discharges into apreheating furnace 8 after being suitably mixed with air or oxygenintroduced through line 9. The feed line for the blast gas I ll passesthrough the furnace where it receives heat from the combustion of theoff-gas before being fed to the tuyeres. Actually in practice thispreheating furnace will be in the form of checker-work ovens which areoperated in sequence on the fire and run principle.

At one side of the blast furnace is an elevated reduction chamber Hwhich is preferably provided with conical ends and with a grid or gratel2 near its lower end. A feed line l3 discharges into the bottom of thereduction chamber. In communication with this feed line is a hopper Mfor finely divided iron ore. Hot reducing gas, such as producer gas,water gas, or the like, is fed into the feed line behind the point ofdischarge of the hopper and picks up the finely divided iron ore andcarries it into the reduction chamber. The leg from the hopper isprovided with a slide valve, star feeder or other suitable controlmember I5. The rate of feed of the powdered ore and of the reducing gasare adjusted relative to each other, the rate of feed of the reducinggas being kept within such limits so as to provide in the reductionchamber I l' a suspension of finely divided material containing at leastabout 5% by volume of solid material. Generally this suspension willcontain from 15 to 25% by volume of solid material which is maintainedin the form of a dense, highly turbulent suspension having theappearance and the properties of a liquid. The reducing gas leaves theupper end of chamber ll through line 16 and enters a cyclone or otherseparator H from which recovered solid material is returned to chamberII by line l8 while the spent reducing gas leaves the system throughline 19.

The temperature in chamber II is maintained below that at which ironbecomes plastic, which will usually be in the range of 900 to 1000 0.Thus a suitable temperature for zone H is between about 700 and 900 C.,the lower limit bein that required to support the reaction between ironoxide and the reducing gas.

It will be understood that the suspension in the reducing chamber IIwill have a level quite analogous to a liquid level. A curved partition20 is arranged along one side of the chamber ll so as to form therein aconduit having its top just below the level of the suspension in thechamber whereby the suspension overflows into this conduit and down intoa standpipe 2i This standpipe is provided with a plurality of spacedjets or nozzles 22 for the introduction into the standpipe of fluidizingquantities of gas. It is preferred that hot reducing gas be used forthis purpose so as to insure completion of the reduction of the ironore. The bottom of the standpipe is provided with a slide valve or starfeeder or other suitable control element 23 which may be manipulated oradjusted to provide for a constant feed of fluidized solid into line 24into which is fed a stream of carrier gas 25. This carrier gas may be aninert gas or, if desired, a portion of the hot blast gas from line I, aportion of the gas from line 1, or off-gas from the preheat ng oven 8,the latter being quite desirable. Line 24 discharges into the blastfurnace at a point adjacent the tuyeres, either slightly above orslightly below, but not at the gas blast, where the temperature ishighest. Preferably, the iron powder is charged to a point as shown inthe drawing.

In general, it will be necessary to supplement the supply of slaggingconstituents, such as lime, in order to accommodate the additionalpurification load on the furnace. This may be provided for by arranginga hop er 26 in communication through a standpipe 2'! with line 24. Thisstandpipe will likewise be provided with suitable jets or nozzles 28 inorder to maintain the solid therein, which will be in a finely dividedstate as heretofore described in a fluidized condition. The feed of thismaterial to line 24 may be regulated by a slide valve. star feeder, orother suitable control element 29 provided near the bottom of thestandpipe 21.

In the practice of the present invention, the operation of the blastfurnace itself is not changed; that is, the conditions above the tuyerelevel remain the same. The charge to the furnace may be selected formost efficient operation in accordance with previous practice. Thetemperature at the tuyeres will be maintained at a level determined bythe type of pig iron desired as well as by the type of ore fed to thefurnace. The only change resides in a more complete recovery of the heatof combustion of the off-gas from the furnace and the supply of thisrecovered heatas preheat to the blast. The blast may be air, airenriched in oxygen, or oxygen.

It will be apparent that many changes may be 75 made in the arrangementheretofore described,

from the scope of the present invention. As heretofore emphasized, thepresent invention is not intended to place any limitation on theoperation of the furnace or to supplant any of the expedients heretoforeadopted for increasing the furnace capacity, but rather to supplementsuch expedients and further increases the capacity of the blast furnace.

The nature and objects of the present invention having thus been setforth and a specific illustrativeembodiment of the same given, What isclaimed .and desired to be secured by Letters Patent is 1. In theoperation of a blast furnace in which ore, coke, and slaggingconstituents are fed to the top thereof in the usual manner and in whicha blast of an oxygen-containing gas is fed to the tuyere level of saidfurnace, the improvement which comprises reducing finely-divided ironore in the form of a fluidized bed in a reduction zone,

6 3. The method of claim 1 in which finely divided slagging constituentsare fed with the finely divided reduced iron ore to the blast furnace.

WARREN K. LEWIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Pages and 111 of FerrousProduction Metallurgy by John L. Bray, published 1942 by John Wiley andSons Inc,

1. IN THE OPERATION OF A BLAST FURNACE IN WHICH ORE, COKE, AND SLAGGING CONSTITUENTS ARE FED TO THE TOP THEREOF IN THE USUAL MANNER AND IN WHICH A BLAST OF AN OXYGEN-CONTAINING GAS IS FED TO THE TUYERE LEVEL OF SAID FURNACE, THE IMPROVEMENT WHICH COMPRISES REDUCING FINELY-DIVIDED IRON ORE IN THE FORM OF A FLUIDIZED BED IN A REDUCTION ZONE, WITHDRAWING REDUCED ORE FROM SAID ZONE AND CHARGING IT IN THE FORM OF AN ELONGATED FLUIDIZED COLUMN TO SAID BLAST FURNACE AT THE TUYERE LEVEL THEREOF FOR THE PURPOSE OF MELTING AND PURIFYING THE LATTER WITHIN THE BLAST FURNACE. 